Unix security

[citation needed] On many UNIX systems, user and password information, if stored locally, can be found in the /etc/passwd and /etc/shadow file pair.

Patching the operating system in a secure manner requires that the software come from a trustworthy source and not have been altered since it was packaged.

Common methods for verifying that operating system patches have not been altered include the use of the digital signature of a cryptographic hash, such as a SHA-256 based checksum, or the use of read-only media.

Firewalls can block access to strictly internal services, unwanted users and in some cases filter network traffic by content.

Other Unix like operating systems may provide their own native functionality and other open source firewall products exist.